DESCRIPTION: The family Rhabdoviridae has members that represent some of the greatest threats to human, animal and plant health, including Rabies virus of humans and animals, Infectious hematopoietic necrosis virus offish, and Rice yellow stunt virus of plants. By comparing the functions of proteins encoded by different rhabdoviruses we hope to fulfill our long-term goal, which is to understand how new viral pathogens emerge via adaptive changes required for replication in different host cells. The proposed experiments will test the hypothesis that phosphorylated "P" proteins encoded by plant negative-strand RNA viruses have novel functions, relative to the cognate proteins from animal viruses, which are required for the successful infection of plant cells. My lab has provided experimental evidence that extends the multiple activities of P to include that of RNA silencing suppressor (RSS). We have also made the novel discovery that this activity can be regulated by its interaction with a second viral protein. The objective of this application is to elucidate the mechanism by which SYNV-P functions as an RSS and how this activity is moderated by interaction with other SYNV proteins. Specific Aim 1: To test the hypothesis that the RSS activity of SYNV-P is mediated via direct binding to RNA. Specific Aim 2: To test the hypothesis that RSS activity is conserved among rhabdovirus P proteins. Specific Aim 3: To test the hypothesis that the RSS activity of SYNV-P can be modulated via interactions with the nucleocapsid (N) or matrix (M) proteins. Additionally, our expertise in purifying N and P protein complexes from insect and bacterial cells will enable us to take advantage of an NIH-funded project at the University of Kentucky that could determine the X-ray crystal structures for these proteins. To date, the structures of the N and P proteins encoded by rhabdoviruses with animal hosts have not been determined. Therefore, if successful, the crystallization of any of these proteins, in homo- or heterogeneous complexes, would represent an important contribution valued by a large community of researchers from different disciplines. In sum, this research is significant for its contribution to the basic understanding of the molecular and cell biology of rhabdoviruses, particularly those of plants, and has the potential to lead to the development of novel control strategies for a variety of diseases. [unreadable] [unreadable] [unreadable]